A word of advice - do your own research, follow the paper trail, and climb your own tree not someone else's. These sites are money making schemes and nobody can "find your family tree" for you. The instructions for cancelling are below (from their site). Follow them exactly and if they continue to bill you, contact your local consumer affairs advisory.

We hope you want to keep your subscription, but if you don’t you must cancel by clicking on the Contact link in the footer of the homepage and choosing Cancellation Requests as the Subject. You cannot just send an email to us to cancel. You must use the Contact Customer Service form.

If you do become a subscriber, at the end of your plan period if you have not cancelled your subscription your credit card will again be charged the then current rate for the plan you have chosen. This ensures you have continuous access to your OneGreatFamily account.